Rechargeable batteries, such as Lithium-ion batteries, experience heating of internal components, e.g., the anode and cathode, during charging. In an instance in which the anode temperature increases above 80 degrees Celsius, there is a possibility that exothermic reactions between the anode and the electrolyte may be initiated, leading to thermal runaway, venting, and/or a fire in the batteries. The charging rate of the batteries may be limited to a predetermined charging rate, such as 0.7 of the capacity of the battery to prevent overheating of the battery. The artificial limiting of the charging rate may significantly increase the time necessary to charge the battery.
In some instances, the actual capacity of the battery may be unknown. This can occur for a variety of different reasons. For example, ageing due to cycle life and calendar life can change the storage and discharge capacity of a battery. Another example is where the battery has been partially discharged to an unknown state. This would make it difficult to know how fast or how much the battery should be recharged to bring it to full capacity. Still another example is where the user may not have any, or accurate, information about the capacity of a given battery. The appropriate amount of charging current or the rate of charging has typically been based upon the capacity of the battery, and without knowledge of the battery's capacity, conservative charging current and charging rates have typically been employed to avoid overheating.
Some have attempted to address the overheating issue by configuring a battery charger to monitor the temperature of one or more batteries or one or more battery cells. The monitored temperature may be used for safety monitoring of the battery during charging, or to limit the charging rate in response exceeding a thermal threshold. However, multiple battery cell systems may only monitor representative cells, such as center and corner cells, low air flow cells, low cooling cells, or other cells which are likely to have higher than average temperatures. The temperatures of the representative cells, or in some cases, models derived from the representative cells may not be indicative of the highest cell temperature. Further, battery cell temperature monitoring is typically of a surface temperature of the monitored battery cells, which may not be indicative of the internal temperature of the battery cell or may have a significant delay. The uncertainties of monitoring reference battery cells and of monitoring battery cell surface temperatures may result in undetected temperature peaks, which may cause damage or failure of one or more battery cells.